I followed the YouTube video tutorial to build a workflow that pushes Google Doc into Pinecone which works fine. Then I created another workflow named "send_email" and calling that in another workflow named "agent". However, when I select the "send_email" workflow in Call n8n Workflow Tool, I see this: "This sub-workflow will not receive any input when called by your AI node. Define your expected input in the sub-workflow’s trigger." Nate did not get this in his video. Any help on what should I do?